1. Field of the Invention
The present invention relates to an optical film and manufacturing method thereof, polarizing plate protective film, polarizing plate and liquid crystal display device.
2. Description of the Related Art
A demand for a liquid crystal display device has been expanded in applications such as a liquid crystal display for an LCD TV or a personal computer. In general, the liquid crystal display device is constituted by a liquid crystal cell and two polarizing plates provided at both sides thereof, in which the liquid crystal cell is obtained by interposing, for example, a transparent electrode, a liquid crystal layer, and a color filter between glass plates. Each polarizing plate is constituted by two optical films (polarizing plate protective films) having a polarizer (which may be referred to as a polarization film) interposed therebetween.
Meanwhile, according to a recent advance in a technology, upsizing of the liquid crystal display device has been accelerated, and at the same time, applications of the liquid crystal display device have been diversified. For example, the liquid crystal display device may be used as a large display installed on the street or in front of a shop or may be used for an advertising display using a display equipment called a digital signage in a public place.
In such applications, since an outdoor usage is envisaged, a deterioration caused by moisture adsorption of a polarizing film may be problem. Thus, it is required to reduce a moisture permeability of the polarizing plate protective film. As for a material having a low moisture permeability, polymethyl methacrylate (hereinafter, may be abbreviated as PMMA) may be exemplified. The PMMA is low in a moisture permeability and further shows an excellence in a transparency or dimensional stability, and thus is used for an optical film.
For example, Japanese Patent Laid-Open Publication No. 2011-16323 discloses a method of manufacturing an acrylic resin film by solution film formation, in which the acrylic resin film may include a crosslinked soft layer polymer showing a rubber elasticity.